Our Moon: the Moon

Introduction

Why doesn’t our Moon have a name? Why do we simply call our Moon the Moon? Shouldn’t we find a better name than just Moon? This theme explores the origin of our Moon’s name across different cultures, and the reasoning behind the IAU’s official recommendations.

The importance of the Moon

People have been naming celestial objects for at least as long as the written word has existed. Almost every civilisation and culture uses names to describe the stars and planets visible to the naked eye, as well as their apparent distribution on the sky (Montmerle, 2013).

From a cultural standpoint, the Moon’s importance to different societies across different eras is universal. Our Moon, as the second-brightest object in the sky after the Sun, has a language equivalent in every known culture, and has been present in mythology, and the focus of scientific research throughout human evolution.

Earth’s own satellite is called the Moon (with a capital M) in both scientific designation and public usage. A natural satellite, a solid object in orbit around a planet, a dwarf planet, a minor planet, or a transneptunian object is sometimes referred to as a moon (with a small m) in public usage.

In Roman mythology, the Moon is Luna, and this Latin origin prevails in Latin-rooted modern languages to this day: Luna in Spanish and Italian, Lune, in French, Lua, in Portuguese, Lună, in Romanian, and so on. Even non-Latin languages such as English have traces of the Latin origin such as the adjective, “lunar.” In Norse mythology Máni is the personification of the Moon, influencing the Swedish, Norwegian, and Danish words for the Moon (Månen). In Hawaiian, the Moon is Mahina, related to the moon goddess Hina. In Hindi, the Moon is चांद (chaand) or Maan in Afrikaans and Inyanga in Zulu. In Chinese and Japanese, the Moon is represented by the same logogram 月, pronounced Tsuki in Japanese and Yuè in Mandarin Chinese.

Public naming of astronomical objects predates any attempt at naming them scientifically. It is only in modern times, with the availability of ever more sophisticated telescopes, that astronomers have needed to establish standardised naming procedures for celestial objects to use in their research (Montmerle, 2013).

Discovering other moons

In January 1610, the Italian astronomer and mathematician Galileo Galilei pointed his telescope toward the planet Jupiter and discovered four of what he referred to as “stars”. All four objects were arranged in a straight line around the planet, and through daily observation Galileo noted that the “stars” weren't “fixed” but moved with the planet — they seemed to move around Jupiter as our own Moon moves around Earth.

Image I - Sample of Sidereus Nuncius drawings of Jupiter and the Medicean Stars. (Original Image courtesy of the History of Science Collections, University of Oklahoma Libraries)

Simon Marius suggested the names Io, Europa, Ganymede, and Callisto (drawn from Greco-Roman mythology) in 1614. While Simon Marius’s choice of names was dismissed at first, by the 20th century, they had grown familiar to the public and entered common usage.

In 1610, humanity’s understanding of the Solar System increased dramatically. The horizons of human knowledge expanded, as our Moon was no longer one of a kind — there were now similar objects orbiting other planets.

The IAU and naming of the Moon

The IAU has been the arbiter of planetary and satellite nomenclature since its inception in 1919, and IAU recommendations rest on well-established scientific facts and have a broad consensus in the astronomical community. The designations of the then major planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto) and the Earth's satellite (Moon) appear in IAU Resolution No. 10, which was approved by the XVIth General Assembly of the IAU in Grenoble, France in 1976. The eight major planets in our Solar System and Earth’s satellite have official IAU names or designations. The designations of the major planets were already in public use when the IAU formed in 1919 (e.g. scientifically, in professional and amateur astronomy literature, in nautical almanacs, etc.). While there are cultural or public names or, simply, names, for the planets and Earth's satellite in other languages, in science there is the need to determine “official” classic names or designations for the major planets and the Moon, which appear in English-language IAU resolutions and the IAU Style Manual (Naming of Astronomical Objects, 2017).

The designation of our Moon is, therefore, the Moon, with a capital M and used as a name (a proper noun). The same applies to the designation of our planet — the Earth, of our Solar System (IAU Style Manual, 1989) and to all the other major planets. At first, it may seem these much-treasured celestial objects don’t have “proper” names. However, it is just the opposite. Calling our Moon the Moon and our Solar System the Solar System reinforces their importance to humanity — they are not just any moon or solar system.